Cardiac arrhythmias, and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrhythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmia, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. In the alternative or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion.
A host of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle, which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
Examples of catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers, such as those disclosed in U.S. Pat. No. 5,617,854 to Munsif, U.S. Pat. No. 4,898,591 to Jang et al., U.S. Pat. No. 5,487,385 to Avitall, and U.S. Pat. No. 5,582,609 to Swanson, the disclosures of which are incorporated herein by reference. The use of particular guiding sheath designs for use in ablation procedures in both the right and/or left atrial chambers are disclosed in U.S. Pat. Nos. 5,427,119, 5,497,119, 5,564,440, and 5,575,766 to Swartz et al., the disclosures of which are incorporated herein by reference.
Less-invasive percutaneous catheter ablation techniques have been disclosed which use end-electrode catheter designs with the intention of ablating and thereby treating focal arrhythmias in the pulmonary veins. These ablation procedures are typically characterized by the incremental application of electrical energy to the tissue to form focal lesions designed to interrupt the inappropriate conduction pathways. Focal ablation methods are intended to destroy and thereby treat focal arrhythmia originating from a pulmonary vein.
U.S. Pat. No. 6,973,339 discloses a lasso catheter for pulmonary vein mapping and ablation. The apparatus for circumferentially mapping a pulmonary vein (PV) comprises a catheter that includes a curved section of a known fixed length, preferably shaped to generally conform to the shape of the interior surface of the PV. The curved section comprises one or more sensing electrodes, and its proximal end is joined at a fixed or generally known angle to a base section of the catheter, or at an angle whose range is limited. Preferably, at least one single-coil five-dimensional position sensors is fixed to the curved section of the catheter. Most preferably, two single-coil five-dimensional position sensors are fixed to the curved section, one at the distal end and one approximately at the center of the curve. A multi-coil six-dimensional position sensor is preferably fixed to the distal end of the base section, proximate to the joint with the curved section. The catheter is inserted into the heart, and the curved section is positioned in essentially continuous contact with the wall of the PV, while the base section remains within the left atrium, typically positioned such that the joint with the curved section is at the ostium of the vein. The information generated by the three position sensors is used to calculate the locations and orientations of the sensing electrodes, which enables mapping of the surface of the PV.
U.S. Pat. Nos. 6,024,740 and 6,117,101 disclose a circumferential ablation device assembly which is adapted to forming a circumferential conduction block in a pulmonary vein. The assembly includes a circumferential ablation element which is adapted to ablate a circumferential region of tissue along a pulmonary vein wall which circumscribes the pulmonary vein lumen, thereby transecting the electrical conductivity of the pulmonary vein against conduction along its longitudinal axis and into the left atrium. The circumferential ablation element includes an expandable member with a working length that is adjustable from a radially collapsed position to a radially expanded position. An equatorial band circumscribes the outer surface of the working length and is adapted to ablate tissue adjacent thereto when actuated by an ablation actuator. The equatorial band has a length relative to the longitudinal axis of the expandable member that is narrow relative to the working length, and is also substantially shorter than its circumference when the working length is in the radially expanded position. A pattern of insulators may be included over an ablation element which otherwise spans the working length in order to form the equatorial band described. The expandable member is also adapted to conform to the pulmonary vein in the region of its ostium, such as by providing a great deal of radial compliance or by providing a taper along the working length which has a distally reducing outer diameter. A linear ablation element is provided adjacent to the circumferential ablation element in a combination assembly which is adapted for use in a less-invasive “maze”-type procedure in the region of the pulmonary vein ostia in the left ventricle.
In addition, various energy delivery modalities have been disclosed for forming such atrial wall lesions, and include use of microwave, laser, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall, as disclosed in WO 93/20767 to Stem et al., U.S. Pat. No. 5,104,393 to Isner et al., and U.S. Pat. No. 5,575,766 to Swartz et al, respectively, the disclosures of which are incorporated herein by reference. U.S. Pat. No. 6,558,375 to Sinofsky, et al., discloses a hand held cardiac ablation instrument and methods for irradiating a target ablation site. The instrument can include at least one light transmitting optical fiber and a light diffusing element to create a circumferential or curvilinear lesion. Light travelling through the light transmitting optical fiber or fibers is scattered in a circular pattern by the light diffusing element. The light diffusing element can include a scattering medium, a reflective end cap, and a reflective surface diametrically opposed to the target ablation site, that interact to provide a substantially uniform distribution of laser radiation throughout the circular target region.
Ablation with cryogens is also known. U.S. Pat. Nos. 7,896,870; 7,951,140 and 8,083,732, each to Arless, et al., disclose catheters having a cryoablation tip with an electrically-driven ablation assembly for heating tissue. The cryoablation tip may be implemented with a cooling chamber through which a controllably injected coolant circulates to lower the tip temperature, and having an RF electrode at its distal end. The RF electrode may be operated to warm cryogenically-cooled tissue, or the coolant may be controlled to conductively cool the tissue in coordination with an RF treatment regimen.
Regardless of the type of catheter used, it is emphasized that particular care must be exercised to ensure that the ablation sites are indeed contiguous; otherwise irregular electrical activity in the pulmonary vein may continue to contribute to atrial arrhythmia. Thus, where ablation of a pulmonary vein has been performed whether with a balloon or lasso catheter or otherwise, a subsequent PV isolation validation often reveals locations or points that have been missed. Typically, a point ablation catheter would then be used to complete the isolation.
Catheters with pressure sensing for detecting tissue contact, facilitating in lesion formation and avoiding perforation of tissue are known. Such catheters may carry a miniature transmitting coil and multiple sensing coils on opposing portions of a flexibly-jointed distal tip section. This design is well-suited for point ablation catheters, but does not lend itself to catheters adapted for tissue contact over an area or at multiple locations, such as with a coil or “lasso” catheter having a distal electrode assembly with a generally circular portion. For these catheters, because the generally circular portion is transverse to the catheter body, the generally circular portion may not exert uniform pressure along its length when an operator applies a distal force on the catheter body to ensure contact between with tissue and the electrodes on the generally circular portion. In particular, the electrodes closer to the catheter body tend to exert greater pressure against the tissue.
Accordingly, each type of catheter has its advantages and disadvantages. Point ablation catheters have distal tip electrodes better suited for point ablation but are time and labor intensive for when ablating larger regions. Circumferential ablation catheters may require less operator skill and less time by enabling multiple contact points simultaneously but they may not easily adapt to variations in anatomy between individual patients. Consequently, a single procedure may require the use of at least two or three catheters for mapping, ablation and electrical/anatomical isolation validation which can significantly increase the cost of the procedure and the duration.
Thus, there is a desire for an electrophysiologic catheter that can provide both point and circumferential mapping and ablation. It is desirable that the catheter have a distal tip electrode for point tissue contact and be capable of adopting a radially expanded configuration for circumferential tissue contact. Moreover, it is desirable that the catheter have improved pressure sensing capabilities to accommodate two- and three-dimensional electrode assemblies with multiple electrode contact points.